1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head including a coil and a magnetic path forming section, the magnetic path forming section being provided for forming a magnetic path for passing a magnetic flux corresponding to a magnetic field produced by the coil.
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system in which signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density when compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a magnetic path forming section. The coil produces a magnetic field corresponding to data to be written on a recording medium. The magnetic path forming section is formed of a magnetic material, and forms a magnetic path for passing a magnetic flux corresponding to the magnetic field produced by the coil. The magnetic path forming section includes a main pole having an end face located in a medium facing surface configured to face the recording medium. The main pole produces, from the aforementioned end face, a write magnetic field for writing the data on the recording medium.
With increases in frequency of write signals to achieve higher recording densities, it is required of the write head unit to provide an improved rate of change in the write magnetic field. To meet such a requirement, it is effective to reduce the length of the magnetic path formed by the magnetic path forming section.
One of approaches to reducing the length of the aforementioned magnetic path is to form the coil in a self-aligned manner, as disclosed in U.S. Pat. No. 8,441,755 B2, for example. The coil formation method disclosed therein is applicable to a write head unit whose structure is such that the magnetic path forming section includes a first magnetic material portion located away from the medium facing surface, a second magnetic material portion spaced from the first magnetic material portion and located between the first magnetic material portion and the medium facing surface, and a coupling portion for coupling the first magnetic material portion and the second magnetic material portion to each other, and the coil includes one or more coil elements located between the first magnetic material portion and the second magnetic material portion. A coil element refers to a portion of the winding of the coil. The first magnetic material portion has a first sidewall facing toward the one or more coil elements. The second magnetic material portion has a second sidewall facing toward the one or more coil elements. The one or more coil elements have a first side surface opposed to the first sidewall, and a second side surface opposed to the second sidewall.
Now, the conventional method for forming a coil in a self-aligned manner will be described in detail. In the conventional method, first, a thin insulating film is formed to cover the first and second magnetic material portions. Then, a seed layer is formed from a conductive material on the insulating film. On the seed layer, formed is a mask having an opening that exposes a portion of the seed layer on which the coil is to be disposed. Part of the edge of the opening is located above the first and second magnetic material portions. The mask is formed by patterning a photoresist layer by photolithography. Using the seed layer as a seed and a cathode, a conductive layer for forming the coil is then formed in the opening of the mask by plating. The conductive layer is formed to include portions that ride over the first and second magnetic material portions. The mask is then removed. Next, unwanted portions of the seed layer, which are portions of the seed layer other than the portion lying under the conductive layer, are removed by wet etching, for example. Next, an insulating layer is formed to cover the conductive layer. The insulating layer, the conductive layer, the first magnetic material portion and the second magnetic material portion are then polished to make their top surfaces even with each other.
According to the conventional method for forming a coil in a self-aligned manner, the coil is formed such that the first side surface and the second side surface of the one or more coil elements are opposed to the first sidewall and the second sidewall, respectively, with the insulating film interposed between the first side surface and the first sidewall, and between the second side surface and the second sidewall. This makes it possible to reduce the length of the magnetic path formed by the magnetic path forming section.
However, the conventional method for forming a coil in a self-aligned manner has the following first to third problems associated with the seed layer.
The first problem will be described first. According to the conventional method, the seed layer is formed to cover the first and second magnetic material portions, and then the mask is formed on the seed layer by photolithography. In the mask forming process, an unpatterned photoresist layer is exposed to light in a predetermined pattern. In the course of the exposure, unwanted reflected light results from the light for exposure being reflected off the portions of the seed layer covering the first and second magnetic material portions. The first problem is that the unwanted reflected light causes a reduction in precision of the mask pattern, which results in a smaller process margin for forming the mask.
Next, the second problem will be described. According to the conventional method, in the step of forming the conductive layer by plating, the conductive layer grows not only from the portion of the seed layer lying between the first and second magnetic material portions but also from the portions of the seed layer covering the first and second magnetic material portions. Consequently, the conductive layer becomes thick in its portions riding over the first and second magnetic material portions. The portion of the conductive layer lying between the first and second magnetic material portions will be polished later into the coil. On the other hand, the portions of the conductive layer riding over the first and second magnetic material portions are unwanted portions, and will thus be removed in the polishing process later.
Attempts to provide the coil with a sufficiently large thickness and attain a sufficiently large polishing margin would increase the thickness of the portions of the conductive layer riding over the first and second magnetic material portions. In such a case, the mask needs to have a large thickness so that the opening of the mask can accommodate the thick conductive layer. This results in a reduced process margin for forming the mask. Further, an increase in the thickness of the portions of the conductive layer riding over the first and second magnetic material portions would increase the amount of polishing that the conductive layer requires in order that such unwanted portions be removed. This results in a reduced process margin for the polishing. The second problem is the reductions in the process margin for forming the mask and the process margin for the polishing.
The third problem relates to the removal of the unwanted portions of the seed layer as described below. According to the conventional method, the unwanted portions of the seed layer include portions of the seed layer covering the first and second magnetic material portions, and thus extend over a large area. The conventional method removes the unwanted portions by, for example, wet etching, which gives rise to problems that the conductive layer is also etched to result in a smaller width of the coil winding, and voids are created inside the coil. The conventional method also has the problem that the unwanted portions of the seed layer may not be completely removed, and the remainder of the unwanted portions may cause a short circuit between a plurality of conductor portions that should be insulated from each other.
In the conventional method, if the removal of the unwanted portions of the seed layer is performed by dry etching such as ion beam etching instead of wet etching, a problem arises. The problem is that, in the step of removing the unwanted portions of the seed layer, flying substances generated by the etching may deposit onto the insulating film that covers the first and second magnetic material portions, thereby forming a redeposit film having conductivity, and the redeposit film may cause a short circuit between a plurality of conductor portions that should be insulated from each other.